1. Field of the Invention
The present invention relates to an operation state detecting circuit for a camera.
2. Description of the Prior Art
The photography operation is started, whether the release operation has been done or not after it has been judged that the power source of the camera is switched on.
In order to detect the photography operation, switches operatively associated with operation members are provided and the state of each switch is detected.
The switch state detecting circuit, constructed as shown in FIG. 1, is known.
In FIG. 1, reference numeral 1 identifies a battery, a switch 100 is operatively associated with the operation member, an inverter circuit 15 is composed of the CMOS, and a pull-up resistor 14 for fixes the gate level of the inverter circuit 15.
In the detecting circuit in FIG. 1, when the switch 100 is closed, a current is supplied to the pull-up resistor 14 to make the level of the input to the inverter circuit 15 low and the output level of the inverter circuit 15 high, while when the switch 100 is opened the input level of the inverter circuit 15 is fixed high and the output level of the inverter circuit 15 is made low by the pull-up resistor 14 in such a manner that the on or off condition of the switch 100 is detected by the output of the inverter circuit 15.
Such a conventional detecting circuit has shortcomings such that power consumption is increased, since current is always supplied to the resistor 14 when the switch 100 is closed.
Furthermore, in order to lower the power consumption when the switch 100 is closed, by eliminating the above shortcomings, it has been proposed as shown in FIG. 2(a) to supply the pull-up resistor 14 with a sampling pulse of a predetermined duty as shown in FIG. 2(b).
In FIG. 2(a), the parts having the same reference numerals as those in FIG. 1 are the same parts. In FIG. 2(a), the sampling pulse as shown in FIG. 2(b) is delivered from a sampling pulse producing circuit 17 to the pull-up resistor 14 via a buffer 16. Furthermore, the sampling pulse producing circuit 17 is connected to an RS Flip-Flop 19 (hereinafter called RSFF 19) to be set with the sampling pulse. Furthermore, the reset terminal of the RSFF 19 is connected to the output terminal of the inverter circuit 15 via an inverter 18. Hereby, the RSFF 19 is constructed with a reset priority.
Because in the circuit shown in FIG. 2(a), when the switch 100 is opened the output level of the inverter circuit 15 is low and a high level is applied to the reset terminal of the RSFF 19 via the inverter 18, the Q output level of the RSFF 19 remains low.
Furthermore, when the switch 100 is closed the output level of the inverter circuit 15 is high and a low level is applied to the reset terminal of the RSFF 19 while the RSFF 19 is reset when the above sampling pulse rises so that the Q output continues to deliver a high level. Thus, also in the this circuit the closed condition of the above switch 100 can be detected by the Q output of the RSFF 19.
In the circuit constructed as shown in FIG. 2(a), when the switch 100 is closed, the current flows through the pull-up resistor 14 only while the level of the above sampling pulse is high so that the power consumption is largely decreased as compared with that shown in FIG. 1.
Taking the power consumption in the above pull-up resistor 14 into consideration, it is sufficient to make the duty of the above sampling pulse small, namely the off time of the pulse in FIG. 2(b) as long as possible as compared with the on time. However, taking the sampling cycle of the switch state into consideration, it is impossible to set the above off time too long.
Namely, when, for example, the above switch 100 is operatively associated with the release operation member of the camera to start supplying current to the light measuring circuit with detection of the switch 100 closing or actuation of the release circuit, the detecting cycle of the switch 100 condition coincides with the sampling cycle at its longest, so that unless the above sampling cycle is set at about 100 msec. at its longest, it takes time to actually start light measuring with the release operation or to start the release operation and therefore there is a danger that the shutter chance might not be obtained.
It is, accordingly, an object of the present invention to eliminate the inconvenience of the above conventional apparatus by making the number of detecting operations per unit time of the detecting operation when detection of the switch condition is necessary or the apparatus is used, greater than ordinary or when the apparatus is not used.
Other purposes and features of the present invention will become apparent from the following description of the embodiment of the present inventin with reference to the accompanying drawings.